Display device and method of manufacturing the same

ABSTRACT

A display device includes an insulating layer disposed on a substrate, a pixel electrode including a first conductive layer, a second conductive layer, and a third conductive layer sequentially stacked on the insulating layer, a pixel defining layer covering the pixel electrode and partially exposing the pixel electrode through an opening, an organic light emitting layer disposed in the opening of the pixel defining layer, and an opposing electrode disposed on the organic light emitting layer and overlapping the pixel electrode. A length of the first conductive layer is less than a length of the second conductive layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to Korean PatentApplication No. 10-2018-0127504 filed on Oct. 24, 2018, the disclosureof which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

Exemplary embodiments of the inventive concept relate to a displaydevice and a method of manufacturing the display device. Moreparticularly, exemplary embodiments of the inventive concept relate to adisplay device capable of improving particle defects and a method ofmanufacturing the display device.

DISCUSSION OF THE RELATED ART

Recently, the importance of flat panel display devices having excellentcharacteristics such as being thin and light weight, and having lowpower consumption, has been increasing. Among flat panel displaydevices, liquid crystal display devices and organic light emittingdisplay devices are widely commercialized because they have excellentresolution and image quality. In particular, organic light emittingdisplay devices are becoming more widely used due to their high responsespeed, low power consumption, and self-luminescence capability.

An organic light emitting display device may include an organic lightemitting device formed in a display area and metal lines formed in aperipheral area neighboring the display area. The organic light emittingdevice may include electrodes and an organic light emitting layerdisposed between the electrodes that emits light.

When a metal layer is formed in the display area and the peripheral areaand an electrode of the organic light emitting diode is formed byetching the metal layer, a metal line and the metal layer may react withthe etchant to cause galvanic corrosion. Galvanic corrosion is aphenomenon in which electrons move and the metal ions are reduced by anoxidation-reduction reaction when two metals having different corrosionpotentials are connected to an electrolyte. Galvanic corrosion may occurwhen the corrosion potential of the metal constituting the metal layerand the metal line differ greatly.

SUMMARY

Exemplary embodiments of the inventive concept provide a display devicecapable of reducing particle defects.

Exemplary embodiments of the inventive concept provide a method ofmanufacturing the display device.

According to an exemplary embodiment of the inventive concept, a displaydevice includes an insulating layer disposed on a substrate, a pixelelectrode including a first conductive layer, a second conductive layer,and a third conductive layer sequentially stacked on the insulatinglayer, in which a length of the first conductive layer is less than alength of the second conductive layer, a pixel defining layer coveringthe pixel electrode and partially exposing the pixel electrode throughan opening, an organic light emitting layer disposed in the opening ofthe pixel defining layer, and an opposing electrode disposed on theorganic light emitting layer and overlapping the pixel electrode.

In an exemplary embodiment, the first conductive layer includes indiumtin oxide (ITO), the second conductive layer includes silver (Ag), andthe third conductive layer includes indium tin oxide (ITO).

In an exemplary embodiment, the display device includes a pad electrodedisposed on the substrate in a non-display area that surrounds a displayarea. The pad electrode includes aluminum (Al).

In an exemplary embodiment, the pad electrode includes a first layer, asecond layer and a third layer which are sequentially stacked. The firstlayer and the third layer include titanium (Ti) and the second layerincludes aluminum (Al).

In an exemplary embodiment, the display devices further includes a thinfilm transistor disposed between the substrate and the pixel electrode.The thin film transistor includes a semiconductor layer, a gateelectrode, a source electrode, and a drain electrode.

In an exemplary embodiment, a length difference between the firstconductive layer and the second conductive layer in an edge portion ofthe pixel electrode is about 190 nm to about 250 nm.

According to an exemplary embodiment of the inventive concept, a methodof manufacturing a display device includes forming an insulating layerin a display area of a substrate, forming a pixel electrode including afirst conductive layer, a second conductive layer, and a thirdconductive layer sequentially stacked on the insulating layer,patterning the third conductive layer of the pixel electrode by etchingthe third conductive layer with a first etchant, patterning the secondconductive layer and the first conductive layer of the pixel electrodeby etching the second conductive layer and the first conductive layerwith a second etchant, forming an organic light emitting layer on thepixel electrode, and forming an opposing electrode overlapping the pixelelectrode on the organic light emitting layer.

In an exemplary embodiment, the method further includes forming a padelectrode in a non-display area of the substrate. The non-display areasurrounds the display area, and the pad electrode includes aluminum(Al).

In an exemplary embodiment, the pad electrode includes a first layer, asecond layer and a third layer which are sequentially stacked, the firstlayer and the third layer include titanium (Ti), and the second layerincludes aluminum (Al).

In an exemplary embodiment, forming the pixel electrode includes formingthe pixel electrode on the pad electrode disposed in the non-displayarea.

In an exemplary embodiment, the first conductive layer includes indiumtin oxide (ITO), the second conductive layer includes silver (Ag) andthe third conductive layer includes indium tin oxide (ITO).

In an exemplary embodiment, in the etching of the third conductivelayer, a length of the first conductive layer in an edge portion of thepixel electrode and in an edge portion of the pad electrode is smallerthan a length of the second conductive layer, respectively.

In an exemplary embodiment, in the etching of the third conductivelayer, an undercut is formed in the first conductive layer in an areacorresponding to an edge portion of the pixel electrode and in an areacorresponding to an edge portion of the pad electrode.

In an exemplary embodiment, in the etching of the second conductivelayer and the first conductive layer, a silver ion generated from thesecond conductive layer is collected in the undercut.

In an exemplary embodiment, a length of the undercut formed in the edgeportion of the pixel electrode is about 190 nm to about 250 nm.

In an exemplary embodiment, a length of the undercut formed in the edgeportion of the pad electrode is about 180 nm to about 200 nm.

In an exemplary embodiment, the method further includes forming a pixeldefining layer. The pixel defining layer covers the undercut of thepixel electrode and has an opening partially exposing the pixelelectrode. The method further includes forming the organic lightemitting layer in the opening of the pixel defining layer.

In an exemplary embodiment, the method further includes forming a thinfilm transistor between the substrate and the pixel electrode. The thinfilm transistor includes a semiconductor layer, a gate electrode, asource electrode, and a drain electrode.

According to an exemplary embodiment of the inventive concept, a displaydevice includes an insulating layer disposed in a display area of asubstrate, a pixel electrode including a first conductive layer, asecond conductive layer, and a third conductive layer sequentiallystacked on the insulating layer. An undercut is formed in an edgeportion of the first conductive layer. The display device furtherincludes a pixel defining layer covering the undercut of the pixelelectrode and having an opening partially exposing the pixel electrode,an organic light emitting layer disposed in the opening of the pixeldefining layer, and an opposing electrode disposed on the organic lightemitting layer and overlapping the pixel electrode.

In an exemplary embodiment, the first conductive layer includes indiumtin oxide (ITO), the second conductive layer includes silver (Ag), andthe third conductive layer includes indium tin oxide (ITO).

According to exemplary embodiments of the inventive concept, a pixelelectrode layer having a stacked structure of ITO/Ag/ITO is patterned byfirst patterning the upper ITO layer with a first etching process andthen patterning the Ag layer and the lower ITO layer with a secondetching process. The amount of silver particles may be reduced throughthe two-step etching process. Therefore, defects that may occur in themanufacturing process caused by the silver particles may be prevented orreduced. In addition, the side surface of a pad electrode may beprevented from being corroded by blocking the reaction with aluminum(Al) included in the pad electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the inventive concept will become moreapparent by describing in detail exemplary embodiments thereof withreference to the accompanying drawings, in which:

FIG. 1 is a plan view illustrating an organic light emitting displaydevice according to an exemplary embodiment.

FIG. 2 is an enlarged view illustrating part A of the display device ofFIG. 1.

FIG. 3 is a cross-sectional view of a display device taken along lineI-I′ and line II-II′ of FIG. 2.

FIGS. 4 to 10 are cross-sectional views illustrating a method ofmanufacturing a display device according to an exemplary embodiment.

FIGS. 11A and 11B are photographs comparing the amount of silverparticles generated in a method of manufacturing a display deviceaccording to an exemplary embodiment and a method of manufacturing adisplay device according to a comparative example.

FIGS. 12A and 12B are photographs comparing an undercut according to anexemplary embodiment and a comparative example.

DETAILED DESCRIPTION

Exemplary embodiments of the inventive concept will be described morefully hereinafter with reference to the accompanying drawings. Likereference numerals may refer to like elements throughout theaccompanying drawings.

FIG. 1 is a plan view illustrating a display device according to anexemplary embodiment.

Referring to FIG. 1, according to an exemplary embodiment, the displaydevice may include a display area DA and non-display area NDA. Thenon-display area NDA may surround the display area DA. A plurality ofpixels PX may be disposed in the display area DA. In the display areaDA, images may be displayed based on light emitted by the plurality ofpixels PX.

The non-display area NDA may include a line area SLA in which aplurality of fan-out lines is arranged and a pad area PDA in which aplurality of pad electrodes formed at end portions of the plurality offan-out lines is arranged.

FIG. 2 is an enlarged view illustrating part A of the display device ofFIG. 1. FIG. 3 is a cross-sectional view of a display device taken alongline I-I′ and line II-II′ of FIG. 2.

Referring to FIGS. 2 and 3, according to an exemplary embodiment, thedisplay device may include a substrate 110, a thin film transistor TFT,an organic light emitting diode OLED, a fan-out line SL and a padelectrode 160.

The substrate 110 includes the display area DA and the non-display areaNDA. The substrate 110 may be a transparent substrate or an opaqueinsulating substrate. For example, the substrate 110 may include glassor plastic such as polyimide (PI), polycarbonate (PC), polyethersulfone(PES), polyethylene terephthalate (PET), polyacrylate, and the like.

A buffer layer 115 may be disposed on the substrate 110. The bufferlayer 115 may block impurities such as oxygen, water, etc. penetratingthrough the substrate 110. In addition, the buffer layer 115 may providea flat surface on top of the substrate 110. The buffer layer 115 mayinclude, for example, silicon nitride, silicon oxide, siliconoxynitride, and the like. Alternatively, the buffer layer 115 may beomitted.

A thin film transistor TFT and an organic light emitting diode OLED maybe disposed on the buffer layer 115 in the display area DA. The thinfilm transistor TFT may include a semiconductor layer 120, a gateelectrode 130, a source electrode 140, and a drain electrode 150. In anexemplary embodiment, the thin film transistor TFT may have a top-gatestructure in which the gate electrode 130 is disposed on top of thesemiconductor layer 120. Alternatively, the thin film transistor TFT mayhave a bottom-gate structure in which the gate electrode is disposedunder the semiconductor layer. Alternatively, the gate electrode mayhave a double-gate gate structure disposed at the top and bottom of thesemiconductor layer 120, respectively.

The semiconductor layer 120 may be disposed on the buffer layer 115. Thesemiconductor layer 120 may be formed of, for example, amorphoussilicon, polycrystalline silicon, an oxide semiconductor, or the like.The semiconductor layer 120 may include a source area, a drain area, anda channel area formed therebetween.

A gate insulating layer 125 covering the semiconductor layer 120 may bedisposed on the buffer layer 115. The gate insulating layer 125 may bedisposed on the substrate 110 in the display area DA and the non-displayarea NDA. The gate insulating layer 125 may insulate the gate electrode130 from the semiconductor layer 120. The gate insulating layer 125 mayinclude, for example, silicon nitride, silicon oxide, siliconoxynitride, and the like.

The gate electrode 130 may be disposed on the gate insulating layer 125.The gate electrode 130 may overlap the channel area of the semiconductorlayer 120. The gate electrode 130 may be formed of a first metal layer.The first metal layer may include a metal such as, for example,molybdenum (Mo), aluminum (Al), copper (Cu), or an alloy of metals.

It will be understood that the terms “first,” “second,” “third,” etc.are used herein to distinguish one element from another, and theelements are not limited by these terms. Thus, a “first” element in anexemplary embodiment may be described as a “second” element in anotherexemplary embodiment.

An interlayer insulating layer 135 covering the gate electrode 130 maybe disposed on the gate insulating layer 125. The interlayer insulatinglayer 135 may be disposed on the substrate 110 in the display area DAand the non-display area NDA. The interlayer insulating layer 135 mayinsulate the source and drain electrodes 140 and 150 from the gateelectrode 130. The interlayer insulating layer 135 may include, forexample, silicon nitride, silicon oxide, silicon oxynitride, or thelike.

The source electrode 140 and the drain electrode 150 may be disposed onthe interlayer insulating layer 135. The source electrode 140 and thedrain electrode 150 may be connected to the source area and the drainarea of the semiconductor layer 120 through contact holes formed in theinterlayer insulating layer 135 and the gate insulating layer 125,respectively. The source electrode 140 and the drain electrode 150 maybe formed of a second metal layer. In an exemplary embodiment, thesecond metal layer may include, for example, aluminum (Al). In anexemplary embodiment, the second metal layer may include, for example,aluminum and an aluminum alloy. The aluminum alloy may include, forexample, any one of copper (Cu), vanadium (V) and silicon (Si).

The second metal layer may include a first layer 161, a second layer 162and a third layer 163 which are sequentially stacked. For example, thefirst layer 161 may be disposed under the second layer 162, and thethird layer 163 may be disposed above the second layer 162. The firstlayer 161, the second layer 162, and the third layer 163 may include,for example, titanium (Ti), aluminum (Al) and titanium (Ti),respectively.

It will be understood that when a component, such as a film, a region, alayer, or an element, is referred to as being “on”, “connected to”,“coupled to”, or “adjacent to” another component, it can be directly on,connected, coupled, or adjacent to the other component, or interveningcomponents may be present. It will also be understood that when acomponent is referred to as being “between” two components, it can bethe only component between the two components, or one or moreintervening components may also be present. It will also be understoodthat when a component is referred to as “covering” another component, itcan be the only component covering the other component, or one or moreintervening components may also be covering the other component.

The display device may further include a storage capacitor disposed inthe display area DA on the substrate 110. The storage capacitor mayinclude a first storage electrode formed of a same first metal layer asthe gate electrode 130 and a second storage electrode formed of a samesecond metal layer as the source and drain electrodes 140 and 150.

A planarization layer 175 may be disposed on the substrate 110. Theplanarization layer 175 may be an insulating layer for planarizing thedisplay area DA in which the thin film transistor TFT is formed. Theplanarization layer 175 may include organic materials such as, forexample, an acrylic resin, an epoxy resin, a polyimide resin, and apolyester resin.

The organic light emitting diode OLED may be disposed on theplanarization layer 175. The organic light emitting diode OLED includesa pixel electrode 180, an organic light emitting layer 210, and anopposing electrode 230. The thin film transistor TFT may be disposedbetween the substrate 110 and the pixel electrode 180.

The pixel electrode 180 may include a first electrode 181, a secondelectrode 182, and a third electrode 183, which are sequentially stackedconductive layers. Thus, the first electrode 181 may also be referred toherein as a first conductive layer, the second electrode 182 may also bereferred to herein as a second conductive layer, and the third electrode183 may also be referred to herein as a third conductive layer.

For example, the first electrode 181 is disposed on the planarizationlayer 175, the second electrode 182 is disposed on the first electrode181, and the third electrode 183 is disposed on the second electrode182.

As shown in FIG. 3, in an exemplary embodiment, as a result of anundercut UDC that is formed during the manufacturing of the displaydevice, which will be described in further detail below, a length of thefirst electrode 181 (the first conductive layer) is less than a lengthof the second electrode 182 (the second conductive layer).

The first electrode 181 may include indium tin oxide (ITO), the secondelectrode 182 may include silver (Ag), and the third electrode 183 mayinclude indium tin oxide (ITO). The second electrode 182 of the pixelelectrode 180 may serve as a main conductive layer. The first electrode181 and the third electrode 183 of the pixel electrode 180 may serve asan auxiliary conductive layer for protecting a lower surface and anupper surface of the second electrode 182, respectively.

A pixel defining layer 190 having an opening exposing the pixelelectrode 180 may be disposed in the display area DA of the substrate110 on which the pixel electrode 180 is disposed. The pixel defininglayer 190 may include an opening exposing an upper surface of the pixelelectrode 180, and a light emitting area of the pixel may be defined asan area in which the opening is formed. The pixel defining layer 190 mayinclude organic materials such as, for example, an acrylic resin, anepoxy resin, a polyimide resin, and a polyester resin.

The organic light emitting layer 210 may be disposed within the openingof the pixel defining layer 190. The organic light emitting layer 210may include a low molecular weight organic compound or a high molecularweight organic compound.

In an exemplary embodiment, the organic light emitting layer 210 mayemit a red light, a green light, or a blue light. In an exemplaryembodiment, when the organic light emitting layer 210 emits a whitelight, the organic light emitting layer 210 may include a multilayerstructure including a red light emitting layer, a green light emittinglayer, and a blue light emitting layer, or may include a single layerstructure including a red light emitting material, a green lightemitting material, and a blue light emitting material.

The opposing electrode 230 may be disposed on the organic light emittinglayer 210 in the display area DA. For example, the opposing electrode230 may be disposed on the organic light emitting layer 210 and thepixel defining layer 190. The opposing electrode 230 may include, forexample, lithium (Li), calcium (Ca), lithium fluoride (LiF), aluminum(Al), magnesium (Mg), or combinations thereof. For example, the opposingelectrode 230 may have an Mg/Ag structure in which magnesium (Mg) andsilver (Ag) are stacked. The opposing electrode 230 may overlap thepixel electrode 180.

The pad electrode 160 formed at an end portion of the fan-out line SLand the fan-out line SL may be disposed on the interlayer insulatinglayer 135 of the non-display area NDA.

The fan-out line SL may be formed of the same first metal layer as thegate electrode 130, or may be formed of the same second metal layer asthe source and drain electrodes 140 and 150.

The pad electrode 160 may be formed of the same second metal layer asthe source and drain electrodes 140 and 150. The pad electrode 160 mayinclude the first layer 161, the second layer 162, and the third layer163 which are sequentially stacked. The second layer 162 of the padelectrode 160 may serve as a main conductive layer. The first layer 161and the third layer 163 of the pad electrode 160 may serve as anauxiliary conductive layer for protecting the lower and upper surfacesof the second layer 162, respectively. The pad electrode 160 may includealuminum (Al). The first layer 161 and the third layer 163 of the padelectrode 160 may include titanium (Ti), and the second layer 162 of thepad electrode 160 may include aluminum (Al).

When the fan-out line SL is formed of the first metal layer, the padelectrode 160 may contact the fan-out line SL through a contact holeformed in the interlayer insulating layer 135. Alternatively, when thefan-out line SL is formed of the second metal layer, the pad electrode160 may be formed integrally with the fan-out line SL.

In an exemplary embodiment, the pixel electrode 180 of the organic lightemitting diode OLED may be patterned by a two-step etch process. Forexample, the third electrode 183 disposed on top of the pixel electrode180 is patterned first by a first etching process using a first etchant.Then, the second electrode 182 and the first electrode 181 disposedunder the third electrode 183 may be simultaneously patterned by thesecond etching process using a second etchant. That is, the thirdelectrode 183 disposed on top of the pixel electrode 180 may bepatterned by a first etching process using a first etchant at a firstpoint in time, and then, the second electrode 182 and the firstelectrode 181 disposed under the third electrode 183 may besimultaneously patterned by the second etching process using a secondetchant at a second point in time occurring after the first point intime.

In an exemplary embodiment, the pixel electrode 180 including silver(Ag) is patterned by the two-step etching process. Therefore, the numberof silver particles generated by silver ions (Ag+) generated in theetching process may be reduced. In addition, as a result of performingthe patterning using the two-step etching process, corrosion of the sidesurface of the pad electrode 160 in which the silver ions (Ag+) aregenerated by galvanic reaction with aluminum (Al) contained in the padelectrode 160 may be reduced. The presence of silver particles may causevarious defects in subsequent processes. For example, the silverparticles may combine with moisture in subsequent processes andgradually proliferate. Therefore, the silver particles may cause adefect that shorts the pixel electrode 180 and the opposing electrode230. In addition, shorting between adjacent pad electrodes 160 mayoccur.

Thus, according to an exemplary embodiment, the pixel electrode 180 isformed by the two-step etching process described herein. As a result ofusing the two-step etching process according to exemplary embodiments,generation of silver particles may be suppressed, and thus, defects thatmay occur during the manufacturing process may be reduced.

FIGS. 4 to 10 are cross-sectional views illustrating a method ofmanufacturing a display device according to an exemplary embodiment.

Referring to FIG. 4, a thin film transistor TFT may be formed in thedisplay area DA of the substrate 110, and a pad electrode 160 may beformed in the non-display area NDA of the substrate 110.

The buffer layer 115 may be formed in the display area DA and thenon-display area NDA of the substrate 110. The buffer layer 115 may beformed by various methods such as, for example, chemical vapordeposition, sputtering, etc. using silicon oxide, silicon nitride,silicon oxynitride, or the like.

The semiconductor layer 120 may be formed in the display area DA of thesubstrate 110 on which the buffer layer 115 is formed. For example, thesemiconductor layer 120 may be formed on the buffer layer 115 in thedisplay area DA of the substrate 110. For example, a semiconductor layer120 may be formed by forming a layer including a silicon-containingmaterial and an oxide semiconductor on the entire surface of the bufferlayer 115, and patterning the layer. When the semiconductor layer 120 ismade of a material including the silicon, an amorphous silicon layer maybe formed on an entire surface of the buffer layer 115 and crystallizedto form a polycrystalline silicon layer. Thereafter, the polycrystallinesilicon layer is patterned and impurity is doped on both sides of thepatterned polycrystalline silicon layer. Thus, a semiconductor layer 120including a source area, a drain area and a channel area therebetweenmay be formed.

The gate insulating layer 125 may be formed in the display area DA andthe non-display area NDA of the substrate 110 on which the semiconductorlayer 120 is formed. For example, the gate insulating layer 125 may beformed on the semiconductor layer 120 and on the buffer layer 115 in thedisplay area DA of the substrate 110, and may be formed on the bufferlayer 115 in the non-display area NDA of the substrate 110. The gateinsulating layer 125 may be formed using, for example, silicon oxide,silicon nitride, silicon oxynitride, or the like.

The first metal layer may be formed on the gate insulating layer 125,and the first metal layer may be patterned to form the gate electrode130 in the display area DA. The gate electrode 130 may overlap thesemiconductor layer 120. The first metal layer may be formed using, forexample, a metal, an alloy of a metal, or the like.

The interlayer insulating layer 135 may be formed in the display area DAof the substrate 110 on which the gate electrode 130 is formed. Forexample, the interlayer insulating layer 135 may be formed on the gateinsulating layer 125 and on the gate electrode 130 in the display areaDA of the substrate 110, and on the gate insulating layer 125 in thenon-display area NDA of the substrate 110. The interlayer insulatinglayer 135 may be formed using, for example, silicon oxide, siliconnitride, silicon oxynitride, or the like.

The interlayer insulating layer 135 and the gate insulating layer 125may form a plurality of contact holes exposing the semiconductor layer120. For example, the contact holes may expose the source area and thedrain area of the semiconductor layer 120, respectively.

A second metal layer is formed on the substrate 110 on which theinterlayer insulating layer 135 is formed, and the second metal layer ispatterned. The second metal layer may be patterned to form the sourceelectrode 140 and the drain electrode 150 in the display area DA and thepad electrode 160 in the non-display area NDA.

The second metal layer may include, for example, aluminum (Al) and analuminum alloy, and the aluminum alloy may include, for example, any oneof copper (Cu), vanadium (V) and silicon (Si).

In an exemplary embodiment, the second metal layer may include a firstlayer 161, a second layer 162, and a third layer 163 that aresequentially stacked. For example, the second metal layer, in which afirst layer including titanium (Ti), a second layer including aluminum(Al), and a third layer including titanium (Ti) are sequentiallystacked, may be formed on the interlayer insulating layer 135.Accordingly, the source electrode 140, the drain electrode 150, and thepad electrode 160 may have a stacked structure of Ti/Al/Ti.

Referring to FIG. 5, a planarization layer 175 is formed on thesubstrate 110 on which the interlayer insulating layer 135 is formed.For example, the planarization layer 175 is formed on the interlayerinsulating layer 135 and on parts of the TFT in the display area DA ofthe substrate 110. The planarization layer 175 may include organicmaterials such as, for example, an acrylic resin, an epoxy resin, apolyimide resin, and a polyester resin. The planarization layer 175 maybe formed to have a thickness that is sufficient to cover the sourceelectrode 140 and the drain electrode 150 formed in the display area DA.

The planarization layer 175 may be patterned to remain in the displayarea DA and removed to expose the pad electrode 160 in the non-displayarea NDA.

Referring to FIG. 6, a pixel electrode layer 180 a is formed on thesubstrate 110 on which the planarization layer 175 is formed. Forexample, the pixel electrode layer 180 a is formed on the planarizationlayer 175 in the display area DA of the substrate 110. In addition, asshown in FIG. 6, the pixel electrode layer 180 a is formed on the padelectrode 160 in the non-display area NDA. The pixel electrode layer 180a includes a first conductive layer 181 a, a second conductive layer 182a, and a third conductive layer 183 a which are sequentially stacked.

The first conductive layer 181 a may include indium tin oxide (ITO). Thesecond conductive layer 182 a may include silver (Ag). The thirdconductive layer 183 a may include indium tin oxide (ITO). Thus, thepixel electrode layer 180 a may have a stacked structure of ITO/Ag/ITO.

A photoresist pattern PRP is formed in the display area DA on thesubstrate 110 on which the pixel electrode layer 180 a is formed. Forexample, the photoresist pattern PRP is formed on the pixel electrodelayer 180 a in the display area DA of the substrate 110. The photoresistpattern PRP may be formed in an electrode area EA in which the pixelelectrode 180 of the organic light emitting diode OLED in the displayarea DA is formed.

Referring to FIG. 7, the third conductive layer 183 a disposed above thepixel electrode layer 180 a is etched through a first etching processusing the photoresist pattern PRP as a mask. The first etchant used inthe first etching process may include, for example, a composition foretching the indium tin oxide (ITO).

The third conductive layer 183 a formed in the display area DA by thefirst etching process is patterned by a third electrode 183 of the pixelelectrode 180. In addition, the third conductive layer 183 a formed inthe non-display area NDA is removed.

In the first etching process, the first etchant penetrates to the secondconductive layer 182 a and the first conductive layer 181 a disposedunder the third conductive layer 183 a. The first conductive layer 181 aincluding the indium tin oxide (ITO), which is the same material as thethird conductive layer 183 a, is partially removed by the first etchingprocess to form an undercut UDC in the first conductive layer 181 a.

Referring to FIG. 8, the pad electrode 160 is formed to have a thicknessof about 6000 Å, and the pixel electrode layer 180 a is formed to have arelatively thin thickness of about 1000 Å. Accordingly, a step coverageof the pixel electrode layer 180 a in a step portion of the padelectrode 160 is poor. The undercut UDC is formed at the step edgeportion of the pad electrode 160 by the first etching process. Thelength of the undercut UDC at the step edge portion of the pad electrode160 may be about 180 nm to about 200 nm. The length of the secondconductive layer 182 a at the step edge portion of the pad electrode 160by the undercut UDC may be longer than the length of the firstconductive layer 181 a.

As shown in FIGS. 7 and 8, etching the third conductive layer 183 ausing the first etching process results in forming the undercut UDC inthe first conductive layer 181 a in an area corresponding to the edgeportion of the pixel electrode 180 and in an area corresponding to theedge portion of the pad electrode 160. Further, etching the thirdconductive layer 183 a results in the length of the first conductivelayer 181 a in the edge portion of the pixel electrode 180 and in theedge portion of the pad electrode 160 being smaller than the length ofthe second conductive layer 182 a.

Referring to FIGS. 8 and 9, the second conductive layer 182 a and thefirst conductive layer 181 a of the pixel electrode layer 180 a areetched through a second etching process using a second etchant. Thesecond etchant may include a composition for etching the silver (Ag) andthe indium tin oxide (ITO).

In the second etching process, silver (Ag) included in the secondconductive layer 182 a is oxidized to generate silver ions (Ag+) 182 b.The silver ions (Ag+) 182 b are collected in the undercut UDC formed atthe stepped portion of the pad electrode 160. Since the silver ions(Ag+) 182 b are gathered in the undercut UDC, the silver ions 182 b maybe prevented from moving toward the pad electrode 160, or the amount ofsilver ions 182 b that move toward the pad electrode 160 may be reduced.

Accordingly, the undercut UDC inhibits migration of the silver ions(Ag+) 182 b. In the second etching process, electrons (−) generated fromaluminum (Al) included in the pad electrode 160 may block the binding ofthe silver ions (Ag+) 182 b. The electrons (−) generated from thealuminum (Al) included in the pad electrode 160 may be prevented frombeing combined with the silver ions (Ag+) 182 b. That is, generation ofsilver particles may be prevented or reduced.

However, some of the silver ions (Ag+) 182 b may still move toward thepad electrode, and these silver ions (Ag+) 182 b are reduced by theelectrons (−) taken from the aluminum (Al) included in the pad electrode160. Thus, silver particles may be generated. However, hydrogen ionsincluded in the second etchant again take electrons (−) from the silverparticles. As a result, the silver particles that have lost electrons(−) may be oxidized again to the silver ions (Ag+) 182 b. Thus, thesilver particles may be prevented from being generated.

As described above, according to exemplary embodiments, the number ofsilver particles generated in the process of forming the pixel electrode180 may be reduced by forming the pixel electrode 180 using the two-stepetching process of the pixel electrode layer 180 a described above. Inaddition, the silver ions (Ag+) may prevent the side surface of the padelectrode 160 from corroding by blocking the reaction with aluminum (Al)included in the pad electrode 160. That is, the side surface of the padelectrode 160 may be prevented from becoming corroded by blocking thereaction with aluminum (Al) included in the pad electrode 160.

The second conductive layer 182 a and the first conductive layer 181 aformed in the display area DA are patterned to the second electrode 182and the first electrode 181 of the pixel electrode 180 by the secondetching process. Accordingly, the pixel electrode 180 of the organiclight emitting diode OLED is formed in the electrode area EA. The edgeportion of the pixel electrode 180 includes an undercut UDC formed inthe first conductive layer 181 a in the first etching process. Thelength of the undercut UDC formed in the first electrode 181 of thepixel electrode 180 may be about 190 nm to about 250 nm. That is, thefirst electrode 181 and the second electrode 182 of the pixel electrode180 may have a length difference in an edge portion of the pixelelectrode 180 of about 190 nm to about 250 nm corresponding to thelength of the undercut UDC. For example, a length difference from anedge portion of the first electrode 181 and an edge portion of thesecond electrode 182 may be between about 190 nm and about 250 nm.

In addition, the second conductive layer 182 a and the first conductivelayer 181 a formed in the non-display area NDA are removed, and the padelectrode 160 is exposed.

After the second etching process is completed, the photoresist patternPRP is removed. In addition, the silver particles remaining on theinterlayer insulating layer 135, the pad electrode 170 and theplanarization layer 175 may be removed through a cleaning process.

Referring to FIGS. 3 and 10, a pixel defining layer 190 covering thepixel electrode 180 may be formed on the planarization layer 175 in thedisplay area DA. The pixel defining layer 190 may be formed of, forexample, a polyimide resin, a photoresist, an acrylic resin, a polyamideresin, a siloxane resin, or the like.

The pixel defining layer 190 may be patterned to form an openingexposing the top surface of the pixel electrode 180. The pixel defininglayer 190 is formed to overlap the undercut UDC formed at the edgeportion of the pixel electrode 180. Thus, the pixel defining layer 190may prevent a display defect due to the undercut UDC of the pixelelectrode.

The organic light emitting layer 210 may be formed in the opening thatexposes the pixel electrode 180. The organic light emitting layer 210may be formed of, for example, a low-molecular organic compound or ahigh-molecular organic compound using a method such as screen printing,inkjet printing, or vapor deposition.

Thereafter, an opposing electrode 220 may be formed on the pixeldefining layer 190 and the organic light emitting layer 210.

The opposing electrode 220 may be formed of, for example, lithium (Li),calcium (Ca), lithium fluoride (LiF), aluminum (Al), silver (Ag),magnesium (Mg), or the like. For example, the opposing electrode 220 mayhave a Mg/Ag structure in which a first layer including magnesium (Mg)and a second layer including silver (Ag) are stacked.

FIGS. 11A and 11B are photographs comparing the amount of silverparticles generated in a method of manufacturing a display deviceaccording to an exemplary embodiment and a method of manufacturing adisplay device according to a comparative example. FIGS. 12A and 12B arephotographs comparing an undercut according to an exemplary embodimentand a comparative example.

According to an exemplary embodiment, the etching process of the pixelelectrode layer having an ITO/Ag/ITO stacked structure includes a firstetching step for first etching an upper ITO layer, and a second etchingstep for simultaneously etching the Ag layer and a lower ITO layer afterthe first etching step, as described above. Results of the exemplaryembodiment are illustrated in FIGS. 11A and 12A and are referred tobelow in Tables 1 and 2.

According to a comparative example 1, the etching process of the pixelelectrode layer having the ITO/Ag/ITO stacked structure simultaneouslyetches the upper ITO layer, the Ag layer and the lower ITO layer. Thatis, in the comparative example 1, a single etching process is performedin which the upper ITO layer, the Ag layer and the lower ITO layer areall simultaneously etched. Results of the comparative example 1 areillustrated in FIGS. 11B and 12B and are referred to below in Tables 1and 2.

According to a comparative example 2, the etching process of the pixelelectrode layer having the ITO/Ag/ITO stacked structure includes a firstetching step for simultaneously etching the upper ITO and the Ag layerand a second etching step for etching the lower ITO layer. Results ofthe comparative example 2 are illustrated below in Tables 1 and 2.

Table 1 compares the occurrence of the silver particles according to theexemplary embodiment and the two comparative examples.

TABLE 1

Pad 

Etch Step 

Ag P/C 

Undercut 

Exemplary Ti/Al/Ti 

(ITO->Ag/ITO) 

Not Occur Embodiment occurring Comparative (ITO/Ag/ITO) 

Occur Not Example 1 occurring Comparative (ITO/Ag->ITO) 

Occur Not Example 2 occurring

Referring to FIG. 11A and Table 1, in the exemplary embodiment, thesilver particle Ag P/C hardly occurs on the pad electrode 160.

Referring to FIG. 11B and Table 1, in the comparative example 1, a largenumber of the silver particle Ag P/C was formed on the pad electrode. Inaddition, in the comparative example 2, a large number of the silverparticle Ag P/C was generated on the pad electrode.

Referring to a relationship between the silver particle Ag P/C and theundercut of the pad electrode 160, the undercut is formed in theconductive layer of the pad electrode 160 in the case of the exemplaryembodiment in which the silver particle Ag P/C does not occur (or barelyoccurs). However, the undercut was not formed in the conductive layer ofthe pad electrode in the case of the comparative examples 1 and 2 inwhich the silver particle Ag P/C was generated in a large number.

Therefore, as can be seen, when the undercut is formed in the conductivelayer of the pad electrode 160, as is done in exemplary embodiments, thesilver particle Ag P/C is not generated (or is barely generated).

Table 2 compares the undercuts according to the exemplary embodiment andthe two comparative examples.

TABLE 2 Undercut 

Pad 

Etch Step 

(Pad Area) 

Exemplary Ti/Al/Ti 

(ITO->Ag/ITO) 

196.7 nm 

Embodiment Comparative (ITO/Ag/ITO) 

106.5 nm 

Example 1 Comparative (ITO/Ag->ITO) 

181.0 nm 

Example 2

Referring to FIG. 12A and Table 2, in the case of the exemplaryembodiment, a length of the undercut UDC formed in the conductive layerof the pad electrode 160 was about 196.7 nm. In the case of thecomparative example 1, a length of the undercut formed in the conductivelayer of the pad electrode was about 106.5 nm. In the case of thecomparative example 2, a length of the undercut formed in the conductivelayer of the pad electrode was about 181.0 nm.

Referring to FIGS. 12A and 12B, the length of the undercut UDC accordingto the exemplary embodiment is about twice that of the undercut UDCaccording to the comparative example 1.

Thus, as can be seen, the length of the undercut of the pad electrodeformed by the two-step etching process of the pixel electrode layeraccording to the exemplary embodiment is about two times more than theundercut of the pad electrode formed by the simultaneous etching processof the pixel electrode layer according to the comparative example 1.Thus, as can be seen, referring to the exemplary embodiment, when thelength of the undercut formed in the conductive layer of the pixelelectrode increases, the number of the silver particles decreases.

As a result, when the undercut is formed in the conductive layer of thepad electrode, the silver particles may be substantially reduced.

According to exemplary embodiments of the inventive concept, the pixelelectrode layer having a stacked structure of ITO/Ag/ITO is patterned byfirst patterning the upper ITO layer with a first etching process, andthen subsequently simultaneously patterning the Ag layer and the lowerITO layer with a second etching process. The number of silver particlesmay be reduced through this two-step etching process. Therefore, defectsthat may occur as a result of the generation of a large amount of silverparticles in the manufacturing process may be removed or reduced. Inaddition, according to exemplary embodiments, the side surface of thepad electrode may be prevented from being corroded by blocking thereaction with aluminum (Al) included in the pad electrode.

Exemplary embodiments of the present inventive concept may be applied toa display device and an electronic device having the display device. Forexample, exemplary embodiments of the present inventive concept may beapplied to a computer monitor, a laptop, a digital camera, a cellularphone, a smartphone, a smart pad, a television, a personal digitalassistant (PDA), a portable multimedia player (PMP), an MP3 player, anavigation system, a game console, a video phone, etc.

While the present inventive concept has been particularly shown anddescribed with reference to the exemplary embodiments thereof, it willbe understood by those of ordinary skill in the art that various changesin form and detail may be made therein without departing from the spiritand scope of the present inventive concept as defined by the followingclaims.

What is claimed is:
 1. A display device, comprising: an insulating layerdisposed on a substrate; a pixel electrode comprising a first conductivelayer, a second conductive layer, and a third conductive layersequentially stacked on the insulating layer in a first direction,wherein an entirety of a length of the first conductive layer is lessthan an entirety of a length of the second conductive layer in a seconddirection crossing the first direction; a pixel defining layer coveringthe pixel electrode and partially exposing the pixel electrode throughan opening; an organic light emitting layer disposed in the opening ofthe pixel defining layer; and an opposing electrode disposed on theorganic light emitting layer and overlapping the pixel electrode.
 2. Thedisplay device of claim 1, wherein the first conductive layer comprisesindium tin oxide (ITO), the second conductive layer comprises silver(Ag), and the third conductive layer comprises indium tin oxide (ITO).3. The display device of claim 1, further comprising: a pad electrodedisposed on the substrate in a non-display area that surrounds a displayarea, wherein the pad electrode comprises aluminum (Al).
 4. The displaydevice of claim 3, wherein the pad electrode comprises a first layer, asecond layer and a third layer which are sequentially stacked, whereinthe first layer and the third layer comprise titanium (Ti) and thesecond layer comprises aluminum (Al).
 5. The display device of claim 1,further comprising: a thin film transistor disposed between thesubstrate and the pixel electrode, wherein the thin film transistorcomprises a semiconductor layer, a gate electrode, a source electrode,and a drain electrode.
 6. The display device of claim 1, wherein alength difference between the first conductive layer and the secondconductive layer in an edge portion of the pixel electrode is about 190nm to about 250 nm.
 7. A method of manufacturing a display device,comprising: forming an insulating layer in a display area of asubstrate; forming a pixel electrode comprising a first conductivelayer, a second conductive layer, and a third conductive layersequentially stacked on the insulating layer, wherein the firstconductive layer comprises indium tin oxide (ITO), the second conductivelayer comprises silver (Ag) and the third conductive layer comprisesindium tin oxide (ITO); patterning the third conductive layer of thepixel electrode by etching the third conductive layer with a firstetchant; patterning the second conductive layer and the first conductivelayer of the pixel electrode by etching the second conductive layer andthe first conductive layer with a second etchant; forming an organiclight emitting layer on the pixel electrode; and forming an opposingelectrode overlapping the pixel electrode on the organic light emittinglayer.
 8. The method of claim 7, further comprising: forming a padelectrode in a non-display area of the substrate, wherein thenon-display area surrounds the display area, the pad electrode comprisesaluminum (Al).
 9. The method of claim 8, wherein the pad electrodecomprises a first layer, a second layer and a third layer which aresequentially stacked, the first layer and the third layer comprisetitanium (Ti), and the second layer comprises aluminum (Al).
 10. Themethod of claim 8, wherein forming the pixel electrode comprises:forming the pixel electrode on the pad electrode disposed in thenon-display area.
 11. The method of claim 7, wherein in the etching ofthe third conductive layer, a length of the first conductive layer in anedge portion of the pixel electrode and in an edge portion of the padelectrode is smaller than a length of the second conductive layer,respectively.
 12. The method of claim 8, wherein in the etching of thethird conductive layer, an undercut is formed in the first conductivelayer in an area corresponding to an edge portion of the pixel electrodeand in an area corresponding to an edge portion of the pad electrode.13. The method of claim 12, wherein in the etching of the secondconductive layer and the first conductive layer, a silver ion generatedfrom the second conductive layer is collected in the undercut.
 14. Themethod of claim 12, wherein a length of the undercut formed in the edgeportion of the pixel electrode is about 190 nm to about 250 nm.
 15. Themethod of claim 12, wherein a length of the undercut formed in the edgeportion of the pad electrode is about 180 nm to about 200 nm.
 16. Themethod of claim 12, further comprising: forming a pixel defining layer,wherein the pixel defining layer covers the undercut of the pixelelectrode and has an opening partially exposing the pixel electrode; andforming the organic light emitting layer in the opening of the pixeldefining layer.
 17. The method of claim 7, further comprising: forming athin film transistor between the substrate and the pixel electrode,wherein the thin film transistor comprises a semiconductor layer, a gateelectrode, a source electrode, and a drain electrode.
 18. A displaydevice, comprising: an insulating layer disposed in a display area of asubstrate; a pixel electrode comprising a first conductive layer, asecond conductive layer, and a third conductive layer sequentiallystacked on the insulating layer, wherein an undercut is formed in anedge portion of the first conductive layer; a pixel defining layercovering the undercut of the pixel electrode and having an openingpartially exposing the pixel electrode; an organic light emitting layerdisposed in the opening of the pixel defining layer; and an opposingelectrode disposed on the organic light emitting layer and overlappingthe pixel electrode.
 19. The display device of claim 18, wherein thefirst conductive layer comprises indium tin oxide (ITO), the secondconductive layer comprises silver (Ag), and the third conductive layercomprises indium tin oxide (ITO).
 20. A method of manufacturing adisplay device, comprising: forming an insulating layer in a displayarea of a substrate; forming a pixel electrode comprising a firstconductive layer, a second conductive layer, and a third conductivelayer sequentially stacked on the insulating layer; patterning the thirdconductive layer of the pixel electrode by etching the third conductivelayer with a first etchant; patterning the second conductive layer andthe first conductive layer of the pixel electrode by etching the secondconductive layer and the first conductive layer with a second etchant;forming an organic light emitting layer on the pixel electrode; andforming an opposing electrode overlapping the pixel electrode on theorganic light emitting layer, wherein in the etching of the thirdconductive layer, an undercut is formed in the first conductive layer inan area corresponding to an edge portion of the pixel electrode.